Dianhydrides find use as intermediates in the preparation of polymeric materials used in a multitude of applications. Considerable attention has been focused recently on the preparation of various polymers such as polyimides and polyamides which can be fabricated into selectively permeable membranes for use in separating gaseous mixtures into their respective components. These polymers are typically prepared by polycondensation of a dianhydride and the corresponding phenylenediamine.
U.S. Pat. Nos. 3,822,202 and 3,899,309 (reissued as Re. 30,351), disclose various polyimides, polyesters and polyamides which are fabricated into semi-permeable membranes for separating various fluids into their respective components. The repeating units of the main polymer chain comprising these polymers have at least one rigid divalent subunit, the two main chain single bonds extending therefrom which are not colinear wherein at least one of the subunits is sterically unable to rotate 360.degree. around such bond. The repeating units also have 50 percent or more of its main chain atoms as members of aromatic rings.
U.S. Pat. No. 4,705,540 discloses highly permeable aromatic polyimide gas separation membranes formed from an aromatic polyimide in which the phenylenediamine groups are rigid and are substituted on essentially all of the positions ortho to the amine functionality and the acid anhydride groups are essentially all attached to rigid aromatic moieties.
U.S. Pat. Nos. 4,717,393 and 4,717,394 disclose polymeric membranes for separating components of a gaseous mixture wherein the membranes are semi-flexible, aromatic polyimides prepared by polycondensation of dianhydrides with phenylenediamines having alkyl substituents on all positions ortho to the amine functionality, or with mixtures of other non-alkylated diamines, some which possess substituents on all positions ortho to the amine functionality. The membranes formed from this class of polyimides are stated to exhibit improved environmental stability and gas permeability.
U.S. Pat. No. 4,378,400 discloses gas separation membranes formed from aromatic polyimides based upon biphenyltetracarboxylic dianhydride for separating various gas mixtures.
A need in the art exists for novel dianhydrides which can be incorporated into polymers for use in applications including, but not limited to, the separation of gaseous mixtures into their respective components.